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Canadian  instituta  for  Historical  Microroproductions  /  Institut  Canadian  da  microraproductions  historiquas 


■j'i'jitri"'-'''-''! '.-'•, 


■i-  ■.'v.-- 


'jL' 


Technical  and  Bibliographic  Notas/Notes  tachniquas  at  bibliographiquas 


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Pagination  is  as   follows:    p. 
La  pagination  est  comme   suit 


[177]-182. 
p.    [1771-182. 


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10X  14X  18X  22X 


26X 


aex 


7  j 


12X 


1«X 


20X 


MX 


28X 


32X 


-  ■?3a^;»m,*<  "i* 


wzsif'^i^wmBJM-msm'-. 


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University  of  Toronto  Archives 


University  of  Toronto  Archives 


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conformity  avec  les  conditions  du  contrat  de 
filmage. 

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papier  est  imprimte  sont  filmAs  en  commen^ant 
par  le  premier  plat  et  en  terminant  soit  par  la 
derniire  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration,  soit  par  le  second 
plat,  salon  le  cas.  Tous  les  autres  exemplaires 
originaux  sont  filmAs  en  commen^ant  par  la 
premiire  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration  et  en  terminant  par 
la  derniAre  page  qui  comporte  une  telle 
empreinte. 

Un  des  symboles  suivants  apparaltra  sur  la 
dernlAre  image  de  cheque  microfiche,  selon  le 
cas:  le  symbole  -^-  signifie  "A  SUIVRE",  le 
symbols  V  signifie  "FIN". 

Les  cartes,  planches,  tableaux,  etc.,  peuvent  Atre 
film6s  ii  des  taux  de  reduction  diffArents. 
Lorsque  le  document  est  trop  grand  pour  Atre 
reproduit  en  un  seul  clichA,  il  est  film*  i  partir 
de  I'angle  supArieur  gauche,  de  gauche  A  droite, 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'images  nicessaire. -Les  diagrammes  suivants 
iilustrent  la  mithode. 


1 

2 

3 

1 

2 

3 

4 

5 

6 

CitmplimtHti  of  tht  AutMtr 


ON  THE  DECAY  OF  EXCITED  RADIOACTIVITY  FROM 
NATURAL  GASES 


BV   MiM   L.    0.    JOHNiON 


[Reprinted  from  the  Physical  Review,  Vol.  XX.,  No.  3,  March,  1905] 


iid^Ws^'riWiti^.'^W!^-:mrr;^*m 


[Kcprinud  fioiii  ili<-  I'liv^n  \\    Ki\1k\v,  \,.|.  \\  ,  N...  j,  M.inh,  |i>i5.J 


On  tiik  DfccAV  ok  Iaiitek  RAnicACTurn  ikum  Naui;ai  ("ia>i>. 

I!V    Ml-   I,.    I!.    I..MN-..\. 

IN  a  rerent  jiajjer  by  I'roftssor  J.  C.  M<  Itnnan  '•  On  the  Radioai  tivily 
of  Mineral  Oils  anil  Natural  (iases"  '  it  was  shown  that  the  natural 
gases  of  Ontario  contain  an  emanation  whiih  is  siniilir  to  tli  il  fuinul 
by  other  investigators  in  the  gases  lontaineil  in  certain  s|)ring  waters  and 
in  the  air  drawn  from  the  surface  layers  of  the  earth,  and  whi<  h,  from 
its  rate  of  decay  as  well  as  that  of  the  radioai  tivity  excited  in  bodies 
exjiosed  to  it,  bears  a  strong  resemblamc  to  the;  emanation  from  railium. 

In  a  i>a]ier  by  Miss  lirooks^  the  rtsiihs  are  jiresented  of  a  scries  of 
measurements  on  the  radiation  from  rods  rendere<i  railioa<  live  by  e\|)Osurc 
to  the  emanation  from  thorium,  radium  and  actinium.  In  this  |.a|ier  it 
s  shown  that,  in  the  case  of  rods  exposed  for  short  perioils  to  the  ema- 

ion  from  thorium  the  radiation  at  first  increases,  reaching  a  maximum 
.1  -■'bout  two  hours  after  removal,  and  then  deiays  ai<  ording  to  an  ex- 
ntial  law.  A  similar  result  was  obtained  w  ilh  rods  exposed  to  the 
eniunation  from  actinium,  the  only  difference  being  that  the  niaximiim 
intensity  with  this  substance  is  reached  in  about  ten  minutes  alter 
removal.  Hut  when  the  rods  were  exposed  to  the  emanation  from 
radium,  it  was  found  for  all  exposures  that  there  was  a  rapid  initial  de- 
crease in  the  intensity  of  the  radiation  for  the  first  ten  minutes  ;  after 
which  it  remained  constant  for  a  length  of  time  which  decreased  with 
the  increase  in  the  i)eriod  of  the  exposure  ;  then  it  droi)pcd  gradually 
and  approached  a  zero  value. 

From  these  results  it  is  evident  that  ai  tivities  excited  in  rods  by  ex- 
posure to  radium,  actinium  or  thorium  have  certain  characteristic  s  by 
which  they  may  be  definitely  distinguished. 

The  experiments  described  in  this  paper  were  c  arried  out  in  order  to 
examine  more  closely  the  emanation  found  in  the  natural  gases  mentioned 
above,  and  to  throw  further  light  on  the  ipiestion  whether  the  radio- 
activity was  due  to  the  presence  of  the  emanation  from  radium  or  due  to 
the  materials  themselves  possessing  the  intrinsic  jiroperty  of  radioactivity. 
The  behavior  of  the  emanation  was  studied  and  a  series  of  curves  obtained 
showing  the  decay  of  the  radiation  due  to  the  excited  activity  on  rods 
exposed  for  different  periods  in  the  gas.  It  was  found  for  all  exposures 
that  the  activity  dropped  at  first  and  reached  a  steady  state  which  length- 
ened as  the  peiiod  of  exposure  was  shortened.  It  then  gradually  died 
down  to  and  approached  a  zero  value.     These  curves  are  ver     similar  to 

'  -Mistract  of  a  paper  presented  at  the  Philadelphia  meeting  of  the  Physical  .'Society  on 
Deceitilier  !o,  1904- 

'  Paper      esented  at  International  Electrii.d  Congress  at  Si.  I  ouis,  Scpltniber,  KJO^. 
3  Philosttphical  Magazine,  .September,  lycH- 


^"Wi .  \.wmm':^irsrr.s'^irf^-ysr'mr"''^KP-  *:sfiis,^'«ipw«5*6»':iff «•■ 


17« 


Tin:  AMiiRiCAX  riivsic.ii.  society. 


[\,.i.,  xx. 


those  yivcn  by  Mis-*  lirooks  for  roils  exposed  to  the  emanation  from 
radium  and,  therefore,  support  the  theory  that  the  emanation  found  in 
the  natural  gases  dealt  with  is  due  to  the  presimce  of  radium  at  their 
source.  Moreover,  I'rofessor  Rutherford  in  his  work  o  •  Radioactivity  '" 
gives  results  showing  that  the  amount  of  acti\  ity  excilcd  on  a  rod  expose<l 
to  the  emanation  from  radium  is  always  directly  jjroportional  to  the 
amount  of  emanation  present.  To  see  if  this  was  true  of  the  active 
emanation  in  natural  gases,  exposures  of  the  s.nne  period  were  made  in 
the  same  gas  on  different  days  and  it  was  found  that,  as  the  activity  of 
the  emanat  on  decreased,  there  was  always  a  proiiortionate  decre.\^e  in  the 
amount  of  activity  uhich  it  exciteil. 

The  gas  under  investigation  was  confined  in  a  cylinder  about  60  cm. 
long  and  25  cm.  in  diameter.  I'.rass  rods  were  suspended  in  the  gas  by 
insulating  supi)orts,  and  conncled  to  ih-  negative  terminal  of  a  I'oepler- 
Holtz  machine,  which  maintained  a  potential  of  11,000  volts.  Alter 
exposure  the  rods  were  inserted  in  a  seiond  receiver  of  the  same  size 
through  which  a  gentle  current  of  air  was  drawn  in  order  to  remove  any 
emanation  adhering  to  them,  Their  activity  was  then  determined  by 
means  of  measurements  upon  the  comluctivity  they  imparted  to  the  air 
in  the  receiver.  These  measurements  were  made  with  a  sensitive  l)ol- 
ezeleck  electrometer,  and  as  the  rods  were  directly  exposed  to  the  air, 
the  conductivity  imparted  by  them  was  due  to  all  the  types  o'i  rays  which 
they  emitted. 

In  the  paper  referred  to  above  by  Professor  Mi  I.ennan  it  was  shown 
that  when  measurements  were  nnde  upon  the  condm  tivity  of  the  gas  as 
it  came  from  the  well,  it  exhibited  a  steaily  decrease,  and  fell  to  one  half 

T.Mii.i:  I. 

Ci'ii.lu  li:  ''v  ,>f  X.iliiril  (/.;  . 


Time. 
Hours.  Minutes. 


Current. 


Arbitrary 
Scale. 


Time. 
Hours.  Minutes. 


Arbitrary 
Scale. 


4 

288 

3 

41 

',41 

7 

292 

10 

340 

IS 

296 

5 

55 

327 

21 

301 

12 

45 

310 

27 

307 

23 

20 

283 

44 

313 

47 

25 

215 

1 

320 

71 

15 

172 

1 

31 

331 

95 

15 

135 

1 

40 

335 

119 

104.5 

2 

46 

340 

145 

78 

'  Ruth<.rforJ.  RiiliaacUviiy,  page  274. 


iiRSEH'IW 


^aki2^  r>.:^ja^'is^:^^- jgf^^?"  .:^^'/ 


nil-  AMi-.Kh.w  rinsiiM.  >i.{iin. 


value  in  al)Oiit  i.-S  days.  In  the  iirt-fnt  in\c>iit:.ition  the  j;as  was 
•  tiulieil  unilrr  slifjlitly  dilTerent  <  iniiiustaiK  l>.  As  sonn  as  it  was  rec  eived 
from  the  «ill  a  rod  was  exposKl  in  it  at  dinVreiit  tunes  and  nnder  nega- 
tive electrification  for  ilitTerent  periods.  The  rod  in  eac  h  e\|iosiire  was 
rendered  active  by  the  deposit  of  the  subslar.ie  caiisui);  evi  ited  radioac- 
tivity, and  it  was  always  found  that  the  removal  of  the  active  rod  was 
followed  by  a  rise  in  the  conductivity  of  the  gas  to  a  n)a\iinum  value, 
after  which  it  gradually  fell  ai  cording  to  an  experimental  law  in  the  same 
manner  as  before.  .\  typical  set  of  observations  on  this  \arialioi;  in  the 
conductivity  is  given  in  Table  I  ,  and  a  curve  representing  them  is  shown 
in  Fig    I. 

In  this  case  a  negatively  charged  rod  was  exposed  at  i  i,ooo  volts  in 
the  gas  for  ten  hours,  and  it  will 
be  seen  from  the  values  given  al  ive 
that  the  conductivity  steadily  rose 
and  reached  a  maximum  value  m 
about  four  hours  after  the  removal 
of  the  negatively  charged  rod.  It 
will  also  be  seen  that  alter  the 
maximum  value  was  reached  the 
conductivity  fell  to  one  half  value 
in  about  seventy  hours. 

In  order  to  investigate  how  the 
activity  excited  in  a  negatively 
charged  rod  varied  with  the  time 
of  ex|)osure,  a  series  of  exposures 
for  different  p  'ods  was  made  on 
one  day  and  tlic  results  of  the^e 
observations  are  given  in  Table  II. 
and  curves  illustrating  them  are 
shown  in  Pig.  2. 

Before  commencing  this  set  of  exposures  a  rod  connected  to  the  nega- 
tive terminal  of  the  electrical  machine  was  susjiended  in  the  gas  for  about 
two  hours.  It  was  then  withdrawn  and  the  t'lrst  exposure  was  made. 
During  the  intervals  which  elapsed  l)ctween  the  different  exposures,  the 
electric  field  was  always  ajiplied  in  the  same  manner  to  the  gas,  with  the 
object  of  making  the  exjwsures  in  the  presenc  e  of  a  freshly  produced 
disintegration  ])roduct. 

The  values  given  in  Table  II.  and  represented  graphically  in  Tig.  2 
show  that  for  all  periods  of  exposure  the  radiation  decreased  initially, 
then  reached  a  steady  state  which  lengthened  as  the  period  of  the 
exposure  decreased,  after  which  it  dropjied  steadily  and  approached  a 
zero  value. 


Fig.    1. 


^^^:m^mmm^^mms^m;^s^\'', ::■■-. m'i'    \  'n,%rpj:istf 


r--% " 


I  So 


nil     AMI.KIiAX  rin: 


II  .socii.iy. 


I\..i    \x. 


T\r,i,i.   II. 


T  wo-i 

11 1  n  M  t  c 

Klvc-ii 

ilr.ute 

Tfn-m 

inut« 

Twenty 

-minute 

Kxp. 

^%UTt. 

Enpo 

»jrr. 

Expoi 

kurc. 

E<)w 

sure. 

Cii'fcnt 

mrrtrt 

Current 

Time  in 
Minute*. 

Current 

'line  tn 
linute^. 

Arbitrary 

Tim«  in 

Mirutf. 

Arburary 

ScaU-. 

Tinre  in 
Miuutes. 

Arbitrary 

Stals. 

Arbitrary 
Scale. 

I 

25.0 

1 

4.H.9 

1 

61.0 

1 

79.5 

2 

18,0 

6 

28.0 

T 

55.0 

-) 

71.5 

7 

0  5 

11 

1').9 

6 

39.5 

5 

56.5 

U.5 

7.0 

!6 

19.3 

U 

32.5 

6 

51.5 

16.5 

4  5 

21 

17.2 

15 

29.0 

11 

49  5 

21.5 

4.0 

31 

16.2 

25 

31.0 

16 

51.0 

26.5 

-■■.il 

36 

14.9 

31 

30.0 

21 

50.5 

31 

4." 

46 

12.0 

37 

31.5 

26 

49.0 

36 

5,0 

51 

11.7 

41 

30.0 

30 

511.0 

41 

4.5 

56 

11.6 

45 

29.0 

36 

44.0 

46 

.?  5 

61 

9.7 

51 

24.0 

40 

44.5 

51 

J.  5 

56 

23.0 

46 

44.5 

61 

3.5 

61 

21.0 

51 
56 
61 

39.5 
36.5 

35  5 

Korty 

-miniitf 

Oni-- 

lOijr 

Two- 

■  hour 

I- our 

•  hour 

Hxp 

osur*' 

tvpu 

S-;  re. 

Expo 

sure. 

E.xposure. 

1 

1:5.0 

4 

154.3 

1 

196.7 

1 

252.3 

-> 

122.0 

7 

141.3 

5 

174.7 

4 

218.3 

6 

102.5 

;i 

130.8 

) 

173.7 

17 

184.3 

11 

96.0 

20 

•  '.i.a 

il 

163.2 

35 

152.3 

16 

91.5 

25 

126.3 

16 

154.2 

42 

137.3 

21 

93.0 

30 

120.3 

26 

148.2 

52 

1243 

26 

90.0 

35 

116.3 

31 

141.7 

60 

108.0 

36 

82.5 

40 

105. S 

36 

134.2 

65 

95.3 

41 

76.0 

45 

100.8 

41 

;  'hi 

69 

89.5 

46 

73.5 

50 

90.8 

46 

113.2 

52 

66.5 

55 

83.3 

51 

108.7 

56 

61.0 

60 

7S.3 

56 

91.7 

61 

56.5 

61 

92.7 

'I  lu'st'  curxf'-  on  a<  i nuiit  u\  iluii  >imilaiity  to  those  of  Miss  ISrook^  lor 
CNposiire  in  the  eniaiintifiii  ol  raihmn  I'oriii  another  link  in  the  i  ham  of 
f\i(!cn(e  whi' h  leads  to  the  conilusioi'.  that  the  emanation  Ibmul  in 
natural  ;_'ases  lias  radiuni  tor  its  sonrce. 

.\s  stated  above  the  results  )i\\t:\\  in  Table  I!,  were  obtained  from 
observations  iii.ide  in  one  day  upon  the  same  i,'as.  Uurini;  this  jieriod  as 
I'ig.  T  shows,  there  was  a  gradual  deeay  of  the  emanation.  To  iletermine 
the  relation  existing;  between  e>ccited  rad  oactivity  and  the  strength  of 
the  emanation  iirodn(  ing  it  a  -eries  of  e\i)Osiires  of  five  minute^  duration 
was  made  on  three  sui  eesive  da\s  in  the  same  gas. 


ifii^l'^JMMSPfS^^m^IJK^^i^' 


N".  ,! 


nil.  .iMi  i\'i  j.y  rins/it!  mhii.j): 


I  Si 


In   m.iNint;   tho-   iiiei->ui     ■iciil^   ihf   <  oiului  tivitv   i>\   tlio   ":i-<  ».!■>   I'lr^t 


made  in  ihc  gas  thii-^  tit-aUMl,  'I'lic  -aim-  |mi)(  icl;iiv  «a^  lollownl  on  fai  li 
(lay  so  as  to  maintain  as  far  as  |M>^>ililo  tlu'  viuio  i  ondition^.  llii'  rLsiilts 
of  tlu'sc  obsorvations  arc  .L;ivt'n  in  ral)lc  III.  wliii  l;  i  ontains  a  nc  ord  ot 
the  dctay  of  tlie  activity  L-M-itcd  on  each  of  the  days. 

T.vi;:.i.    HI. 

l-'.\-.il.;l   l\,!./h<.i.ti:  ilv  (l-'r.    -miniitr  l^yf'  ll'(    i. 


Column  I. 

1  First  Day  ■. 

Ctjlumn  H. 

Time 
1  Minutes. 

Current 
1  Arbitrary- 
Scale  . 

Time 
in  Minutes. 

1.52 

no.  2 

1.5 

4 

7l).2 

9 

S 

o7  2 

10 

10 

40.2 

15 

IS 

J7.2 

2'.) 

20 

3H.7 

24 

25 

39.2 

30 

31 

.3S.X 

35 

35 

3S.8 

4') 

40 

37.3 

45 

45 

33.8 

59 

SO 

31.3 

hi 

55 

30.3 

60 

31.8 

Current 
Arbitiary 
Seal     . 

Time 
in  Minutes 

90 

1.5 

4iJ 

2.5 

32 

10 

30 

15 

35 

20 

34 

25 

35.6 

30 

31.1 

35 

30.1 

40 

30.1 

45 

26.1 

55 

23.1 

60 

Column  III,     Third  Day.. 

Current 

I  Arbitrary 

Scale   . 

64.5 

55.5 

24.5 

27.5 

2'i 

28.5 

28  5 

27.5 

25.5 

25 

19 

20 


wm 


l82 


THE  AMEKICAX  Pf/yS/CAL   .S0C/E1Y. 


[Vol.  XX. 


The  strength  of  the  emanation  jiresent  in  the  gas  on  each  day  is  given 
in  Table  iV. 

TAIiI.E    IV. 


Exposure. 


First  ilay 

Second  d.iy. 
Third  d.iy.... 


Strength  of  EniKnKtion. 

476 
394 
320 


From  an  inspection  of  these  values  together  with  the  results  in  Table 
III.  it  will  he  seen,  that  a  direct  proportionality  e.xists  between  the 
strength  of  the  emanation  and  the  amount  of  activity  excited. 

Taiii.e  V. 

E.xtiltii  A'lhfii'ihfi:  ify  {Ei:'e-iiifiititt'  Jijc/^osiirt'). 


Time  in  Minutes. 

Column  I, 
First  D«y) 
Current. 

Column  II. 

(Second  Day) 

Current. 

Column  III. 

(Third  Day) 

Current. 

1 

110 

108 

94.8 

10 

40.2 

38.4 

36 

20 

38.7 

42 

41.1 

35 

38.8 

37.3 

40.4 

40 

37.3 

36.1 

37.4 

45 

33.8 

36.1 

36.7 

Table  V.  contains  a  few  of  the  results  reduced  on  this  basis.  The 
values  of  the  activity  obtsined  in  the  first  day  are  recorded  in  Column  I. 
and  the  intensity  of  the  emanation  is  assumed  to  be  unity.  Columns  11. 
and  III.  contain  the  readings  obtained  on  the  second  and  third  days  cor- 
rected to  an  emanation  of  unit  intensity.  The  general  agreement  of  the 
values  recorded  in  the  three  columns  justify  the  assumption  of  the  law  of 
proportionality. 

In  the  experiments  tiescrilied  in  this  jiaper  the  effects  found  were  jiro- 
duced  by  all  the  rays  given  off  from  the  excited  body.  Experiments 
are  now  in  progress  to  investigate  these  effects  still  further  and  especially 
to  determine  the  decay  curves  on  the  basis  of  ,s  and  ;-  radiations. 


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